A liquid crystal display indispensably requires polarizing elements disposed on both sides of a liquid crystal cell because of an image forming method adopted therein and generally polarizing plates are adhered. Besides, on a liquid crystal panel, various kinds of optical elements have been used in addition to a polarizing plate in order to improve a display quality of a display. For example, there have been used a retardation plate for coloration prevention, a viewing angle increasing film for improving a viewing angle of a liquid crystal display and a brightness enhancement film for raising a contrast of a display. The films each are collectively referred to an optical film.
A pressure-sensitive adhesive is usually employed in adhering an optical film described above to a liquid crystal cell. An optical film and a liquid crystal cell or optical films are usually adhered to each other using a pressure-sensitive adhesive therebetween in order to reduce a light loss. In such cases, a pressure-sensitive adhesive optical film in which a pressure-sensitive adhesive is provided in advance on one surface of an optical film as a pressure-sensitive adhesive layer is generally used because of a merit such as that no necessity arises for a drying step of fix the optical film.
The image display such as a liquid crystal display in which the pressure-sensitive adhesive optical film is applied is used in various environments. Therefore, the pressure-sensitive adhesive optical film is required to have durability such as heat resistance in a high temperature environment and humidity resistance in a high humidity environment. As a pressure-sensitive adhesive for a polarizing film and a glass substrate of a liquid crystal cell in which such durability is improved, it is proposed to use a pressure-sensitive adhesive including a (meth)acrylic resin in which 0.3 to 10% by weight of an amino group and/or amide group-containing (meth)acrylic monomer component is copolymerized (see Patent Literature 1 listed below).
On the other hand, in recent years, a thin-model image display has been desired, and, therefore, a thin-model pressure-sensitive adhesive optical film also has been desired. With such a thin-model product has been demanded, a thin-model pressure-sensitive adhesive layer of the pressure-sensitive adhesive optical film also has been demanded. However, as the pressure-sensitive adhesive layer is formed thin, it becomes difficult to satisfy durability. Even when the pressure-sensitive adhesive disclosed in Patent Literature 1 is used, it becomes impossible to satisfy durability, as the pressure-sensitive adhesive layer is formed thin.
Patent Literature 1: JP-A No. 06-108025